As a safety measure, athletes involved in many types of sports, such as football and hockey, typically wear protective gear such as helmets to avoid injuries. Typical helmets are designed and structured to protect the athlete's head from a head-on frontal or top collision but are not designed to protect stresses on the brain. These helmets typically include a cushioning layer of material within the helmet shell which is held between the athlete's head and the helmet shell to absorb at least some of the impact force.
Although such equipment typically functions as designed for head-on or frontal impacts which the user often expects and can brace for, the equipment is not ideally structured to protect the brain from impact forces when the athlete is knocked directly backwards or sideways onto the rear or crown of the head and has no ability to brace for or cushion the fall. Recently, there have been a number of well publicized injuries to amateur and professional athletes in sports such as football and hockey where the individual may be tackled or checked and forced to fall straight back or sideways, thus directly impacting the back or side of the head. Accordingly, there is a need for an improved protective helmet which protects the brain from injury caused by impact at non-frontal angles such as backwards or adjacent to the top of the head.
When an individual is knocked backwards or sideways the fall is typically not cushioned resulting in direct impact on the helmet, which force is translated to the person's head. In such a direct impact the brain suffers an abrupt deceleration from its falling momentum and may suffer from inertial loading within the person's skull leading to linear or rotational compression and shear. One method of rating such impact force as a function of deceleration and time is called the Head Injury Criterion (HIC). It is believed that HIC values over 1,000 typically represent the onset of moderate to severe brain injury and HIC values between about 850-1000 can result in a mild brain injury such as a concussion. HIC levels below about 700 are not severe enough to cause mild brain injury. One discussion of the mechanics of head injury and the HIC is provided in, Elson, Lawrence M., Ph.D. and Ward, Carley C., Ph.D., "Mechanisms and Pathophysiology of Mild Head Injury,"Seminars In Neurology, March 1994: p.8-18.
One suggestion in prior helmets has been a cushion or pad within a helmet shell or on the exterior, protecting the top or front of the helmet. These pads are made from compressed fabric, rubber, sponges or rigid Styrofoam.RTM. multicellular material permanently mounted to the shell. The pads are intended to be used for the life of the helmet. The thicker the pad the better the absorption; however, to avoid an oversized helmet and/or discomfort to the user, the size of such pads is limited. In standard hockey or football helmets vinyl nitrile is used, whereas in bicycle helmets solid Styrofoam.RTM. material with sponge rubber is used.
When interior pads absorb an impact force they are compressed. The pads typically spring back into place; however, the material is worn with each such impact and over time the absorption power deteriorates. This deterioration is difficult to notice visually, especially when the material is inside of the helmet or a fabric cover. Once deterioration occurs, the helmet does not provide the protection originally intended.
An alternate teaching has been to mount a compressible material over the exterior of a helmet, such as described in U.S. Pat. No. 4,937,888 to Strauss. Although this provides a thicker combination of padding, the material still transmits the impact force after the material is completely compressed. Deterioration in the impact absorption ability of such a material is also difficult to observe visually. Further, the material thickness described in the Straus patent is primarily situated to protect the user from a frontal impact.
Any protective material absorbs only so much impact force by compression. When this compression force is exceeded, the material either reaches a density where it transmits the force without further absorption or the material is crushed, absorbing additional energy. Once the material is crushed it needs to be replaced. When the material is within a helmet or within a covering the crushed material is difficult to notice. Thus there is a risk that a helmet will be used despite the protective material being no longer able to efficiently absorb an impact.
Finally, as is well understood, when a larger and thicker impact absorbing pad or combination of pads is used, more time is taken for deceleration which reduces the impact force which is transferred to the user, minimizing potential traumatic injury. Methods of extending the deceleration time are needed.
The present invention addresses these concerns.